Although cystic fibrosis is a multiorgan disease the most severe symptoms are found in the respiratory tract. This inherited disease is characterized by an ion transport imbalance, principally caused by a defective chloride secretion mediated by a mutated cystic fibrosis transmembrane conductance regulator (CFTR) and excessively increased Na⁺-absorption via the amiloride-sensitive epithelial Na⁺ channel (ENaC). To circumvent one of these basic problems of CF we tried to significantly reduce the Na⁺ hyperabsorption by using specific siRNA targeting ENaCa.

We used primary cultured human nasal epithelia cells that were transfected with siRNA. To prove the functional inhibition of ENaC expression we employed modified Ussing chambers. The Na⁺ absorption through ENaC was assessed as short-circuit current (I_SC) and conductance (G_t) in presence of amiloride after siRNA transfection. Using this method we also analyzed the dose- and time-depended effect of the siRNA used. Furthermore, we carried out biochemical Western Blot analyses with a specific ENaC antibody.

Statistical evaluation revealed that the siRNA is able to inhibit the functional ENaC by about 69% compared to the controls. We demonstrated that the siRNA is able to sustain this functional ENaC inhibition over a time period of 72h.

Furthermore, we showed a 63% suppression of the a-ENaC protein by Western blot analyses in siRNA transfected cells compared to the controls. From these data we conclude, that the ENaC specific siRNA could have a benefit for the CF related symptoms of the patients and therefore could turn out to be a potential therapy option.